Overgrazing

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Overgrazing occurs when plants are exposed to intensive grazing for extended periods of time, or without sufficient recovery periods. It can be caused by either livestock in poorly managed agricultural applications, or by overpopulations of native or non-native wild animals.

Overgrazing reduces the usefulness, productivity, and biodiversity of the land and is one cause of desertification and erosion. Overgrazing is also seen as a cause of the spread of invasive species of non-native plants and of weeds.

Overgrazing is used as the canonical example of the Tragedy of the commons.[1] Sustainable grassland production is based on grass and grassland management, land management, animal management, and livestock marketing. Grazing management, with sustainable agriculture and agroecology practices, is the foundation of grassland-based livestock production since it affects both animal and plant health and productivity.[2]

Contents

Process

Overgrazing can occur under continuous or rotational grazing. It can be caused by having too many animals on the farm or by not properly controlling their grazing activity. Overgrazing reduces palatable plant leaf areas, which reduces interception of sunlight and plant growth. Plants become weakened and have reduced root length, and potentially the pasture sod can be weakened although in many locales overgrazing results in an increased sod vigour dominated by unpalatable grasses. The reduced root length makes the plants more susceptible to death during dry weather. A weakened sod allows weed seeds to germinate and grow.[citation needed]

Indicators

One indicator of overgrazing is that the animals run short of pasture. In some regions of the United States under continuous grazing overgrazed pastures are predominated by short-grass species such as bluegrass and will be less than 2-3 inches tall in the grazed areas. In other parts of the world overgrazed pasture is typically taller than sustainably grazed pasture, with grass heights typically over 1 meter and dominated by unpalatable species such as Aristida or Imperata. In all cases palatable tall grasses such as orchard grass are sparse or non-existent. In such cases of overgrazing soil may be visible between plants in the stand, allowing erosion to occur, though in many circumstances overgrazed pastures have a greater sward cover than sustainably grazed pastures.

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